Polyphenylene ethers are known and described in numerous publications including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875. Polyphenylene ethers can be combined with vinyl aromatic resins, e.g., styrene resins, to provide thermoplastic compositions having many properties improved over those of either polyphenylene ether resin or styrene resin alone. See Cizek, U.S. Pat. No. 3,393,435. Polyphenylene ether-vinyl aromatic resin compositions can be made by forming a mixture of polyphenylene ether resin and the vinyl aromatic compound, see, for example, Fox, U.S. Pat. No. 3,356,761; Bostick and Hay, U.S. Pat. No. 3,522,326; and U.K. Pat. No. 1,264,889.
In a copending application (Attorney's Docket GE-429 (8CH-2122/2154)), filed concurrently herewith by applicants herein, is described an improved process to make a polyphenylene ether-methylene chloride solid complex. In the process, methylene chloride is used as a combined solvent for polymerization and as a precipitant for the polyphenylene ether product. Typically, 2,6-xylenol is oxidatively coupled to produce a resin at elevated temperature (&lt;40.degree. C.) under oxygen pressure, the polymerization catalyst is extracted from the hot solution with aqueous acid or a chelating agent, and then the mixture is cooled. The polymer precipitates as a complex with methylene chloride and is removed by filtration or centrifugation. In the application above-mentioned, the polymer complex is washed with methylene chloride to remove quinones and other low molecular weight reaction products, and sometimes with water to complete removal of the catalyst. The wet cake is then heated to break up the complex and drive off methylene chloride and water--producing dry, amorphous polyphenylene ether powder suitable for blending, e.g., with other ingredients, such as styrene resins, glass fiber fillers, flame retardant agents, stabilizers, pigments and other conventional molding resin components.
It has now been discovered, and is the subject matter of the present invention, that the drying step can be eliminated and compositions comprising polyphenylene ethers and vinyl aromatic resins can be prepared from the wet cake by suspending it in monomeric vinyl aromatic compounds and heating gently to break the complex and distill off methylene chloride (and water). After the methylene chloride (and water) has been removed, the temperature of the mixture may be increased to bring about polymerization of the vinyl aromatic compound. Of course, catalysts can be added, if desired, to increase the polymerization rate. When enough of the monomer has been polymerized to provide the desired composition ratio, the composition of two resins is isolated by crumbing in hot water, spray drying, devolatizing in an extruder, or other conventional procedures, and any excess of vinyl aromatic compound can be recovered for recycling.
In comparison with conventional coextrusion techniques, the compositions provided by the present process are made without costly blending and compounding equipment, and high extrusion temperatures--and the possibility of polymer degradation, color formation, and the like--are avoided.
The process of this invention can be used with the polymer-methylene chloride complex produced by washing the cake with methylene chloride to remove low molecular weight impurities. Altenatively, it can be used with the "crude" wet cake, i.e., the highly colored polyphenylene ether-methylene chloride complex prepared by washing the cake with water to remove catalyst--but not colored impurities. In the latter case, the final product is a light colored composition of polyphenylene ether and poly (vinyl aromatic), because of a considerable reduction in color which occurs during polymerization of the vinyl aromatic component.